The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
The tooth or teeth simply need time to recover from the trauma. It's when the pressure sensitivity is persistent that you should suspect something like a break, crack, or decayed tooth and should see your dentist. Sensitivity to temperature usually means teeth have been compromised in some way.